Nitrocellulose-based propellant compositions are well known in the art, having wide ranging utility in the military, aerospace, and civilian industries. For example, such propellant compositions are used as smokeless explosive charges for artillery and small arms, for solid fuel rocket engines, and in blasting compositions employed within the construction industry.
Conventional granular, nitrocellulose-based propellant compositions typically include nitrocellulose, selected organic or inorganic salts for use as ballistic modifiers or stabilizers, and other additives such as carbon black. When other energetic bases such as nitroguanidine or nitroglycerin are also added, the propellant is considered a “multiple base” propellant. Increasing the number of energetic bases within the propellant provides an effective means to enhance the muzzle velocity of the charge and thereby increase performance of the propellant.
Thus, a “single-base” propellant contains nitrocellulose with optional additives. A “double-base” propellant contains nitrocellulose as well as an additional nitroglycerin component. A “triple-base” propellant generally contains nitrocellulose, nitroglycerin, and another base such as nitroguanidine. For example, a double-base propellant is obtainable from Hercules Incorporated of Wilmington, Del., marketed and sold under the tradename Bullseye® Powder. Bullseye® Powder has a 40% nitroglycerin content, 0.75% ethylene centralite (stabilizer), 1.25% potassium sulfate (anti-glare agent), 0.40% graphite glaze and the balance nitrocellulose, the nitrocellulose having a nitrogen content of about 13.2%.
The production of conventional single-base, double-base, or triple-base propellant powders are known in the art such as set forth in U.S. Pat. No. 4,701,228 and U.S. Pat. No. 3,622,655, which are incorporated herein by reference. The basic steps according to those processes is to dissolve a dehydrated nitrocellulose in ether-alcohol or other solvent. After solvation, a selected number of additives, and if desired, nitrated oil and stabilizer, are added. The resultant slurry is cast and cured at an elevated temperature of about 43° C. to about 68° C. until a solid propellant mass is formed. The resultant dough is drawn and extruded into sheets, pulverized into the form of grains, filled into a mold, freed from liquid and dried to yield a conventional double-base explosive powder.
U.S. Pat. No. 3,907,619 discloses double-base cast propellants formulated with nitrocellulose, nitroglycerin, triacetin, tolylene diisocyanate, and nitrodiphenylamine. This patent discloses casting solvents consisting of nitrodiphenylamine, diglycol dinitrate, and the like.
U.S. Pat. No. 4,080,411 discloses casting powders where the solvents are ether, ethyl alcohol, and acetone in a ratio of 60:35:5. Similarly, U.S. Pat. No. 4,701,228 discloses casting powders produced using solvents of ether or “acetone-alcohol.”
U.S. Pat. No. 5,218,166 recites the use of Bullseye® Powder from Hercules, a double-base of nitrocellulose and nitroglycerin.
Casting powders containing nitrocellulose have thus been formulated generally by incorporating additives and stabilizers, such as 2-nitrodiphenylamine (2-NDPA), to alcohol-wet nitrocellulose. Nitroglycerin is added as a solution with the solvent diethyl ether and the stabilizer 2-NDPA, and mixed in a mixer. Additional diethyl ether is added to give a total solvent loading of approximately 100%. A small amount (e.g., 1%) of pulling solvent, such as acetone, is added at the end of the mixing stage to promote nitrocellulose fibers adhering to each other through the finishing stages of blocking, billeting, finish pressing and cutting. This process is applicable to mix batches of over 200 pounds in a 100 gallon mixer.
The process known in the art, relying on diethyl ether, suffers from several disadvantages. One disadvantage is the requirement for large quantities of the expensive and hazardous solvent diethyl ether. In a typical 220 pound mix batch prepared conventionally as described above, fully 165 pounds of diethyl ether is used, along with 55 pounds of ethanol. The binary solvent achieves a 100% solvent load in a ratio of 3:1 diethyl ether to ethyl alcohol. Another disadvantage is that nitroglycerin, which is typically purchased from a third party, is typically shipped in the solvent acetone. Accordingly, the use of acetone during shipping renders the nitroglycerin unsuitable for use, directly, in the above process where one desires to manufacture a casting powder and propellant containing nitroglycerin.
The art is in need of a process for producing casting powders and multiple-base propellants, which overcomes the disadvantages of previously used processes. In particular, the art is in need of a process that allows for a significant reduction in the use of diethyl ether, and the direct use of nitroglycerin formulated in acetone. Applicant's invention unexpectedly addresses these needs.